In-situ chemical-mechanical planarization pad metrology using ultrasonic imaging

ABSTRACT

Chemical-mechanical planarization (CMP) apparatus and methods for detecting polishing pad properties using ultrasonic imaging is presented. An ultrasonic probe assembly transmits ultrasonic signals onto the surface of a polishing pad during a CMP process. Reflected ultrasonic signals are collected and analyzed to monitor polishing pad properties in real-time. This allows CMP process adjustments to be made during the CMP process.

BACKGROUND OF THE INVENTION

This invention relates to apparatus and methods of chemical-mechanicalplanarization using ultrasonic imaging. More particularly, thisinvention relates to a chemical-mechanical planarization pad metrologyapparatus that transmits an ultrasonic signal onto the surface of apolishing pad to monitor polishing pad properties in real-time.

Fabricating integrated circuit devices is a complex multi-step processthat creates structures with various electrical properties to form aconnected set of devices. Multiple layers of conducting, semiconducting,dielectric, and insulting materials are deposited on a substrate duringintegrated circuit device fabrication. As these devices become smallerand more densely packed, more levels of photolithography and additionalprocessing steps are often required.

Often, imperfect substrate fabrication and imperfect integrated circuitlayer deposition result in formation of undesirable topography (e.g.,recesses, protrusions, scratches, etc.) on the substrate and on one ormore of the deposited layers. Because undesirable topography cancompromise the integrity of an integrated circuit device (e.g., atopographical recess in a dielectric layer can impose step coverageproblems for the deposition of another integrated circuit layer, andundesirable topology can cause depth of focus issues duringphotolithography), the substrate and each deposited layer of anintegrated circuit device are preferably planarized (i.e., made level)before additional layers of integrated circuit material are deposited.

A common technique used to planarize the surface material of anintegrated circuit wafer is chemical-mechanical planarization (“CMP”).Known CMP processes are used to remove undesirable topology from layersof integrated circuit material. The rotating polishing pad mechanicallypolishes (i.e., removes undesirable topography from) the surfacematerial of the integrated circuit wafer. Concurrently, a fluid-basedchemical (i.e., a chemical polishing “slurry”) is dispensed onto thesurface of the polishing pad to facilitate the removal of undesirabletopography. Chemical polishing slurry may react with the integratedcircuit material. That is, the slurry chemically weakens surfacematerial of the wafer so that the surface is more easily removed by themechanical abrasion of the polishing pad. Chemical polishing slurry mayalso be an inert liquid applied to the polishing pad. The inert liquidfacilitates the removal of mechanically-ground integrated circuitmaterial.

As device dimensions continue to scale down, CMP processes become morecritical in the process flow. For example, polishing actions should beperformed such that scratches or other defects do not appear on thesurface of the polished integrated circuit wafer. Furthermore, in orderto achieve uniform planarity, a constant polishing rate should bemaintained. Thus, polishing pad maintenance plays a significant role indiminishing the drawbacks of the CMP process.

It has been shown that polishing pad properties, such as pad roughness(or texture), pad groove depth (which determines pad wear and paderosion), pad density, pad thickness, and elastic modulus, influence CMPremoval rates and uniform planarity. However, information that relatespolishing pad properties to polishing performance is sparse because ofinadequate measurement techniques.

Currently, surface topography measurements are obtained using knownoptical systems, such as a laser scanning microscope. However, there aresignificant drawbacks with the use of a laser scanning microscope.First, the CMP pad must be cleaned and dried before it can be examinedwith the microscope, which is a time-consuming and inefficient process.Also, because scanning laser microscopes are cumbersome, the examinationprocess is performed offline (i.e., outside of the CMP tool), which isalso a time-consuming and inefficient process. Furthermore, because CMPpads are typically semi-translucent, scanning laser microscopes andother known optical systems have difficulty resolving scratches andpolishing pad defects.

In view of the foregoing, it would be desirable to collect polishing paddata and transmit the collected data in real-time to a processor suchthat process adjustments may be made during a CMP process.

It would also be desirable to maximize wafer throughput (i.e., thenumber of wafers processed per unit of time) while determining andmonitoring polishing pad properties.

It would further be desirable to provide an apparatus for in-situ CMPpad metrology that uses ultrasonic imaging.

SUMMARY OF THE INVENTION

It is an object of this invention to collect polishing pad data andtransmit the collected data in real-time to a processor such thatprocess adjustments may be made during a CMP process.

It is also an object of this invention to maximize wafer throughputwhile determining and monitoring polishing pad properties.

It is a further object of this invention to provide an apparatus forin-situ CMP pad metrology that uses ultrasonic imaging.

In accordance with this invention, an apparatus and method for polishingpad metrology using ultrasonic imaging is provided that determines andmonitors polishing pad properties and allows real-time processadjustments to a CMP process.

In a preferred embodiment of the invention, ultrasonic imaging isperformed by an ultrasonic probe assembly, which preferably includes anultrasonic source and an ultrasonic detector. The ultrasonic probeassembly transmits ultrasonic signals onto the surface of a polishingpad. While some of the transmitted ultrasonic signals propagate throughthe polishing pad, other transmitted ultrasonic signals are reflectedfrom the surface of the polishing pad and are collected by theultrasonic detector. The reflected ultrasonic signals are analyzed inreal time to provide real-time monitoring of the polishing pad as itpolishes. For example, upon correlating the reflected ultrasonic signalswith polishing pad position data from which the measurement was taken,contour maps and cross-sectional pad profiles can be obtained. Also,real-time pad properties, such as pad wear and pad erosion can beobtained from the reflected ultrasonic signals.

In some embodiments, the data collected while monitoring the polishingpad as it polishes may be transmitted to, for example, engineers,computer software, or apparatus that generates statistical processcontrol (SPC) charts. Based at least in part on the collected data,real-time process adjustments may be made. For example, the processrecipe may be automatically adjusted to compensate for pad wear or paderosion, thus extending the life of a polishing pad and improving waferthroughput.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the invention will beapparent upon consideration of the following detailed description, takenin conjunction with the accompanying drawings, in which like referencecharacters refer to like parts throughout, and in which:

FIG. 1 is a schematic diagram of an embodiment of a CMP apparatus forin-situ monitoring of polishing pad properties according to theinvention;

FIG. 2 is a flowchart of an embodiment of a method of monitoringpolishing pad properties and then adjusting a CMP process based on themonitored properties according to the invention;

FIG. 3 is a graph of time of flight of ultrasonic signals versuspolishing pad position for a polishing pad;

FIG. 4 is a graph of reflectivity versus polishing pad position for apolishing pad;

FIG. 5 is a reflection image of the surface of a polishing pad;

FIG. 6 is a time of flight surface profile image created from collectedposition data and time of flight data of a polishing pad;

FIG. 7 is a graph of time of flight of the ultrasonic signals versuspolishing pad position for a polishing pad immersed in deionized water;

FIG. 8 is a graph of reflectivity versus polishing pad position for apolishing pad immersed in deionized water;

FIG. 9 is a reflection image of the surface of a polishing pad immersedin deionized water; and

FIG. 10 is a time of flight surface profile image created usingcollected position data and time of flight data of a polishing padimmersed in deionized water.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides CMP pad metrology apparatus and methods forin-situ determination and monitoring of polishing pad properties usingultrasonic imaging during a CMP process.

Ultrasonic imaging uses a focused ultrasonic signal transmitted onto thesurface of a polishing pad. While ultrasonic imaging is widely used inthe medical industry (e.g., non-invasive imaging of a fetus) and in theaerospace industry (e.g., defect detection in structures), ultrasonicimaging can also be advantageously used in the semiconductor industryfor monitoring polishing pad properties during a CMP process.

Ultrasonic imaging differs from other well-known optical imaging methodsbecause it does not require sample preparation (e.g., polishing padsthat are cleaned and dried) and because it provides a non-destructivemethod for determining physical properties, microstructure, andtopography images. Ultrasonic probes are also portable andcost-effective. Even further, ultrasonic imaging can be applied to allstates of matter except plasma. For example, unlike known opticalimaging methods, propagation of an ultrasonic signal through a materialis not affected by the material's transparency or opacity. Becausepolishing pads are typically semi-transparent, known optical imagingmethods typically have difficulty resolving surface defects.

In accordance with the invention, apparatus and methods are provided forpolishing pad metrology using ultrasonic imaging that determines andmonitors polishing pad properties and allows real-time processadjustments to a CMP process.

FIG. 1 illustrates an embodiment of CMP apparatus having ultrasonicimaging for in-situ monitoring of CMP pad properties in accordance withthe invention. CMP apparatus 100 has a platen 102 and a polishing pad104. Platen 102 and polishing pad 104 are driven by a drive assembly 110to move with translation motions 106 and rotation motions 108. Polishingpad 104 may be a conventional polishing pad made from a relatively soft,thin, and porous material, such as polyurethane. Polishing pad 104 mayalso be an abrasive polishing pad with abrasive particles fixedly bondedto a suspension medium. CMP apparatus 100 may also have an underpad 109attached to the surface of platen 102 for supporting polishing pad 104.

To planarize a substrate 114, a conditioning head assembly 116 pressessubstrate 114 against polishing pad 104 in the presence of fluid-basedpolishing chemical 112. As used herein, “substrate” includes a baselayer (e.g., a silicon wafer, a semiconductor material, or an insulatingmaterial) and may include one or more integrated circuit layersdeposited on the base layer. Conditioning head assembly 116 may bedriven to move backwards and forwards by a conditioning arm 118. Platen102 and conditioning head assembly 116 move relative to one another totranslate substrate 114 across the surface of polishing pad 104. As aresult, the rotating polishing pad 104 mechanically polishes (i.e.,removes undesirable topography from) the surface material of substrate114. Concurrently, a fluid-based polishing chemical 112 (i.e., achemical polishing “slurry”) is dispensed onto the surface of polishingpad 104. Chemical polishing slurry 112 may react with the surface ofsubstrate 114. In other embodiments, chemical polishing slurry 112 maybe an inert liquid applied to the polishing pad to facilitate theremoval of undesirable topography. For example, deionized water appliedto the interface between polishing pad 104 and substrate 114 mayfacilitate removal of mechanically-ground integrated circuit material.

CMP processes should consistently and accurately produce a uniformlyplanar surface on the substrate in order to precisely fabricateintegrated circuit devices. However, polishing pad 104 typically wearsunevenly as it is used, thus affecting its removal rate. The removalrate of integrated circuit material varies based at least in part on ageand erosion (i.e., pad wear) of polishing pad 104. For example,polishing pad 104 may be substantially more worn at the center of thepad than at the edge of the pad. Performing a CMP process on a substratewith such a non-uniform polishing pad results in non-uniformlyplanarized substrates. Thus, polishing pad 104 is preferably“conditioned” as part of the CMP process in order to restore polishingpad 104 to its original removal rate. When polishing pad 104 can nolonger be conditioned, polishing pad 104 should be replaced.

As repeated CMP processes are performed, the properties of polishing pad104 should be observed. Such properties may include, for example, padroughness (i.e., texture), pad groove depth (which determines pad depthand pad erosion), pad density, pad thickness, and elastic modulus. Tomonitor and determine these polishing pad properties, CMP apparatus 100also includes an ultrasonic probe assembly 120 and a computer processor124. Ultrasonic probe assembly 120 preferably has a diameter betweenabout 3 millimeters and 50 millimeters. Processor 124 preferably has animage processing card 126 and a data acquisition card 128.

Although a single ultrasonic probe assembly 120 is shown, multipleultrasonic probe assemblies may be positioned within CMP apparatus 100to facilitate monitoring of polishing pad properties.

In one embodiment, ultrasonic probe assembly 120 has a conventional“contact” ultrasonic transducer, where the interface medium betweenpolishing pad 104 and ultrasonic probe assembly 120 is a suitable liquidor liquid gel material. In an alternative embodiment, ultrasonic probeassembly 120 has a “non-contact” ultrasonic transducer, in which thereis no interface medium (i.e., air/gas) between polishing pad 104 andultrasonic probe assembly 120 (a vacuum exists).

Ultrasonic probe assembly 120 preferably includes an ultrasonic source130 and an ultrasonic detector 132 for transmitting and receivingultrasonic signals. Ultrasonic source 130 is configured to transmit anultrasonic signal at an area on the surface of polishing pad 104 assubstrate 114 is being polished. Note that transmitting and receivingultrasonic signals may also be performed between polishing steps (e.g.,between wafers or lots). Ultrasonic probe assembly 120 preferablycontacts chemical polishing slurry 112. While chemical polishing slurry112 may be any suitable slurry, chemical polishing slurry 112 ispreferably deionized water to provide an interface medium which iseasily controllable and repeatable (e.g., it can be maintained at aconstant temperature, has well-known properties, and is readilyavailable). Note that if ultrasonic probe assembly 120 has a“non-contact” ultrasonic transducer, ultrasonic probe assembly 120 isnot in contact with chemical polishing slurry 112.

As shown in FIG. 1, ultrasonic probe assembly 120 is preferably fixed toconditioning arm 118. In other embodiments, ultrasonic probe assembly120 may be fixed to other suitable structures within CMP apparatus 100,such as conditioning head assembly 116, a slurry arm (not shown), or anoverhead fixed ring (not shown). Processor 124 may be configured todirect conditioning arm 118 to move backwards and forwards over thesurface of polishing pad 104 during the CMP process. The advantage offixing ultrasonic probe assembly 120 to conditioning arm 118 is thatprocessor 124 can calculate the real-time position of ultrasonic probeassembly 120 based at least in part on the position of conditioning arm118. Furthermore, because conditioning arm 118 moves backwards andforwards across the diameter of polishing pad 104, which preferablyrotates at a constant velocity, processor 124 can determine real-timepolishing pad properties for a substantial portion of polishing pad 104.

If desired, CMP apparatus 100 may include sensors (not shown) to obtainposition data of ultrasonic probe assembly 120. The sensors may be fixedto conditioning arm 118 or another suitable structure. The sensorstransmit position data to processor 124. In response to receivingposition data from the sensors, processor 124 correlates the collectedposition data with the collected ultrasonic signals.

Ultrasonic source 130 transmits ultrasonic signals onto the surface ofpolishing pad 104. Some ultrasonic signals may be absorbed (e.g., intochemical polishing slurry 112). Some ultrasonic signals may propagatethrough polishing pad 104 and be subsequently reflected from platen 102.(Platen 102 is preferably a metal, such as aluminum, which is anexcellent reflector of ultrasonic signals). Some ultrasonic signals mayreflect off of polishing pad 104. In response to ultrasonic detector 132receiving reflected ultrasonic signals, ultrasonic probe assembly 120transmits the reflected ultrasonic signals to an ultrasonic amplifier122, which amplifies the signals before processing. The amplifiedreflected ultrasonic signals are then transmitted to processor 124 todetermine the polishing pad properties for a particular position onpolishing pad 104.

FIG. 2 shows an illustrative method 200 for determining and monitoringthe properties of polishing pad 104 using ultrasonic probe assembly 120.At step 202, a user selects a process “recipe” using computer processor124 or other suitable processor that can control CMP apparatus 100. Asused herein, a process recipe includes a set of polishing parametersthat can be varied to achieve control of the CMP process. Such a processrecipe may be, for example, a polish recipe, a conditioning recipe, orany other suitable recipe. Process parameters may include, for example,the downward force applied by conditioning head assembly 116, theduration of the polishing operation performed by conditioning headassembly 116, the amount of backforce pressure used to secure substrate114 to conditioning head assembly 116, the rotational velocity ofconditioning head assembly 116, the oscillation of conditioning headassembly 116, or any other appropriate process parameters. In otherembodiments, the user may manually create a customized process recipe.For example, the user may create a polishing recipe by inputting desiredprocess parameters into processor 124.

In response to selecting or inputting a process recipe, substrate 114 isloaded onto CMP apparatus 100 at step 204. In some embodiments, CMPapparatus 100 may include a loading/unloading assembly (not shown). Acassette, holding at least one substrate, may be placed at theloading/unloading assembly. In response to CMP apparatus 100 detectingthe presence of a cassette at the loading/unloading assembly, CMPapparatus 100 transfers substrate 114 from the cassette to conditioninghead assembly 116 using a robot, a wafer transport arm, or othersuitable wafer carrier.

At step 206, the CMP process begins. In particular, conditioning headassembly 116 holding substrate 114 is driven backwards and forwards overthe surface of polishing pad 104. As a result, the rotating polishingpad 104 mechanically polishes the surface material of substrate 114.Concurrently, the chemical polishing slurry 112 is dispensed onto thesurface of polishing pad 104.

While the CMP process is being performed (i.e., in-situ), ultrasonicsource 130 transmits ultrasonic signals onto the surface of polishingpad 104 at step 208. In other embodiments, ultrasonic source 130transmits ultrasonic signals onto the surface of polishing pad 104 aftersubstrate 114 is polished (e.g., ex-situ). Some transmitted ultrasonicsignals may be reflected from polishing pad 104, while others maypropagate through polishing pad 104 and be subsequently reflected fromplaten 102. Ultrasonic detector 132 receives reflected ultrasonicsignals at step 210. At step 212, the reflected ultrasonic signals areamplified by ultrasonic amplifier 122. The amplified signals are thentransmitted to computer processor 124.

As computer processor 124 receives real-time reflected and amplifiedultrasonic signals, computer processor 124 monitors the properties ofpolishing pad 104 at step 214. At substep 216, processor 124 determinesreal-time pad properties based at least in part on the reflected andamplified ultrasonic signals. For example, in response to receivingultrasonic signals reflected from polishing pad 104 and ultrasonicsignals reflected from platen 102, processor 124 may calculate thethickness of polishing pad 104. As shown in FIGS. 3–10, processor 124may generate ultrasonic images and various graphs based at least in parton the collected ultrasonic signals.

As shown in FIGS. 3–10, ultrasonic probe assembly 120 preferably has thecapability of resolving at least micron-sized polishing pad features,thus allowing processor 124 to measure pad properties, such as padroughness (or texture), pad groove depth, and other physical padproperties.

FIG. 3 shows the measured round-trip travel time (i.e., time of flight)of ultrasonic signals for a polishing pad versus position for anon-contact ultrasonic signal transmitted over 50 millimeters of thepolishing pad. From the graph shown, processor 124 can determine thethickness of the polishing pad and pad groove depth. Processor 124 canalso create a cross-sectional profile of the polishing pad.

FIG. 4 shows a graph of reflectivity versus position for a non-contactultrasonic signal transmitted over 50 millimeters of the polishing pad.Reflectivity is determined by calculating the area underneath aparticular transmission or reflected peak. In FIG. 4, the higher thereflectivity, the smoother the surface. Thus, FIG. 4 illustrates thesurface roughness of the polishing pad.

FIGS. 5 and 6 show a reflection image and a time of flightsurface-profile image generated using position data and time of flightmeasurements. At a position along the scan, processor 124 estimates thedepth of any feature that reflects the ultrasonic signal based at leastin part on the time of flight of the ultrasonic signal. The ultrasonicdetector operates with a time gate chosen so that its output indicatesthe amplitude of the ultrasonic signal reflected from the polishing padat that particular position. Once the scan has been completed, processor124 processes the position data and the associated depth and amplitudedata into a single three-dimensional graph that shows both depth andamplitude as functions of position. In particular, FIGS. 5 and 6 providea real-time topography image of the polishing pad.

Note that while FIGS. 3–6 were performed using a non-contact transducer(i.e., no interface medium), the ultrasonic probe assembly may alsoresolve polishing pad features while the polishing pad is immersed in aninterface medium. For example, FIGS. 7–10 show a time of flight versusposition graph, a reflectivity versus position graph, a reflectionimage, and a time of flight surface profile image, respectively, for apolishing pad immersed in deionized water.

Returning to FIG. 2, in response to processor 124 monitoring theproperties of polishing pad 104, processor 124 may automatically adjustthe process recipe (selected at step 202) based at least in part on thedetermined real-time pad properties. Automatically adjusting the processrecipe improves throughput while optimizing polishing parameters. Forexample, processor 124 may automatically adjust the downward polishforce or other polishing parameters to compensate for pad wear.Processor 124 may also notify the user when polishing pad 104 requireschanging (e.g., based on pad wear monitoring).

The determined real-time pad properties (e.g., surface topography maps,pad thickness measurements, etc.) may also or instead be transmitted tothe user. Alternatively, statistical process control (SPC) charts may begenerated based on the pad properties. The user can then manually adjustthe process recipe.

Although the invention is described herein in terms ofchemical-mechanical planarization, the invention is also applicable tomechanical planarization of substrates.

Thus it is seen that ultrasonic signals may be used with CMP apparatusto determine and monitor polishing pad properties and to providereal-time process control. One skilled in the art will appreciate thatthe invention can be practiced by other than the described embodiments,which are presented for purposes of illustration and not of limitation,and the invention is limited only by the claims which follow.

1. A method of monitoring chemical-mechanical polishing pads, the methodcomprising: transmitting ultrasonic signals onto the surface of apolishing pad using a contact ultrasonic transducer, wherein theultrasonic signals are transmitted onto the surface of the polishing padthrough a chemical polishing slurry and a portion of the ultrasonicsignals are reflected; detecting the reflected ultrasonic signals; andprocessing the reflected ultrasonic signals, wherein the processingcomprises measuring the reflectivity of the surface of the polishing padto determine roughness of the polishing pad.
 2. The method of claim 1wherein the processing comprises generating a surface topography imageof the polishing pad based at least in part on the reflected ultrasonicsignals.
 3. The method of claim 1 further comprising automaticallyadjusting a chemical-mechanical planarization process recipe based atleast in part on the processed reflected ultrasonic signals.
 4. A methodof monitoring chemical-mechanical polishing pads, the method comprising:receiving a chemical-mechanical planarization process recipe; polishinga substrate with a polishing pad based on the received process recipe;transmitting ultrasonic signals onto the surface of the polishing padwhile simultaneously polishing the substrate, wherein a portion of theultrasonic signals are reflected; collecting the reflected ultrasonicsignals; processing the reflected ultrasonic signals, wherein theprocessing comprises measuring the reflectivity of the surface of thepolishing pad to determine roughness of the polishing pad; and adjustingthe process recipe based at least in part on the determined roughness ofthe polishing pad.
 5. The method of claim 4 wherein the process recipeis a polishing recipe.
 6. The method of claim 4 wherein the processrecipe is a conditioning recipe.
 7. The method of claim 4 wherein theprocessing comprises generating a surface topography image of thepolishing pad based at least in part on the reflected ultrasonicsignals.
 8. The method of claim 4 wherein the adjusting comprises usinga computer processor to automatically adjust the process recipe based atleast in part on the determined roughness of the polishing pad.
 9. Themethod of claim 4 further comprising issuing a notification when thepolishing pad requires replacement.
 10. A method of monitoringchemical-mechanical polishing pads, the method comprising: receiving achemical-mechanical planarization process recipe; polishing a substratewith a polishing pad based on the received process recipe; transmittingultrasonic signals onto the surface of the polishing pad, wherein aportion of the ultrasonic signals are reflected; collecting positiondata for each transmitted ultrasonic signal substantially simultaneouslywhile transmitting the ultrasonic signals; collecting the reflectedultrasonic signals; correlating the collected position data with thereflected ultrasonic signals; and generating surface topography imagesusing the collected position data and the reflected ultrasonic signals,wherein the generating comprises measuring the reflectivity of thesurface of the polishing pad to generate the surface topography images.11. A method of monitoring chemical-mechanical polishing pads, themethod comprising: receiving a chemical-mechanical planarization processrecipe selected by a user; polishing a substrate with a polishing padbased on the selected process recipe; immersing the substrate andpolishing pad in deionized water; transmitting ultrasonic signals ontothe surface of the polishing pad simultaneously while polishing, whereina portion of the ultrasonic signals are reflected; detecting thereflected ultrasonic signals; processing the reflected ultrasonicsignals, wherein the processing comprises measuring the reflectivity ofthe surface of the polishing pad to determine roughness of the polishingpad; and adjusting the process recipe based at least in part on thedetermined roughness of the polishing pad.
 12. The method of claim 11wherein the adjusting comprises using a computer processor toautomatically adjust the process recipe based at least in part on thedetermined roughness of the polishing pad.
 13. The method of claim 11wherein the process recipe is a polishing recipe.
 14. The method ofclaim 11 wherein the process recipe is a conditioning recipe.
 15. Themethod of claim 11 wherein the processing comprises generating a surfacetopography image of the polishing pad.
 16. The method of claim 11wherein the processing comprises generating a statistical processcontrol chart.
 17. A method of monitoring chemical-mechanical polishingpads, the method comprising: receiving a chemical-mechanicalplanarization process recipe; polishing a substrate with a polishing padbased on the selected process recipe; transmitting ultrasonic signalsonto the surface of the polishing pad simultaneously while polishing,wherein a portion of the ultrasonic signals are reflected; detecting thereflected ultrasonic signals; processing the reflected ultrasonicsignals, wherein the processing comprises measuring the reflectivity ofthe surface of the polishing pad to determine roughness of the polishingpad; and receiving adjustments to the process recipe during thepolishing.
 18. The method of claim 17 wherein the processing comprisesgenerating a surface topography image of the polishing pad.
 19. Themethod of claim 17 wherein the processing comprises generating astatistical process control chart.
 20. A method of monitoring substratepolishing pads, the method comprising: transmitting ultrasonic signalsonto the surface of a polishing pad, wherein a portion of the ultrasonicsignals are reflected; detecting the reflected ultrasonic signals;processing the reflected ultrasonic signals to monitor the polishingpad, wherein the processing comprises measuring the reflectivity of thesurface of the polishing pad to generate a surface topography image ofthe polishing pad based at least in part on the reflected ultrasonicsignals.
 21. A method of monitoring substrate polishing pads, the methodcomprising: receiving a process recipe; polishing a substrate with apolishing pad based on the received process recipe; transmittingultrasonic signals onto the surface of the polishing pad whilesimultaneously polishing the substrate, wherein a portion of theultrasonic signals are reflected; collecting the reflected ultrasonicsignals; processing the reflected ultrasonic signals, wherein theprocessing comprises measuring the reflectivity of the surface of thepolishing pad to determine physical properties of the polishing pad,wherein determining the physical properties comprises generating asurface topography image of the polishing pad based at least in part onthe reflected ultrasonic signals; and adjusting the process recipe basedat least in part on the determined physical properties of the polishingpad.
 22. The method of claim 1 wherein the chemical polishing slurrycomprises deionized water.
 23. The method of claim 1 wherein theprocessing comprises generating a cross-sectional pad profile based atleast in part on the reflected ultrasonic signals.
 24. The method ofclaim 1 wherein the processing further comprises resolving approximatelymicron-sized properties of the polishing pad.
 25. The method of claim 4wherein the transmitting further comprises using a contact ultrasonictransducer to transmit ultrasonic signals onto the surface of thepolishing pad through a chemical polishing slurry.
 26. The method ofclaim 25 wherein the chemical polishing slurry comprises deionizedwater.
 27. The method of claim 4 wherein the processing comprisesgenerating a cross-sectional pad profile based at least in part on thereflected ultrasonic signals.
 28. The method of claim 4 wherein theprocessing further comprises resolving approximately micron-sizedproperties of the polishing pad.
 29. The method of claim 10 wherein thetransmitting further comprises using a contact ultrasonic transducer totransmit ultrasonic signals onto the surface of the polishing padthrough a chemical polishing slurry.
 30. The method of claim 29 whereinthe chemical polishing slurry comprises deionized water.
 31. The methodof claim 10 wherein the processing comprises generating across-sectional pad profile based at least in part on the reflectedultrasonic signals.
 32. The method of claim 10 wherein the processingfurther comprises resolving approximately micron-sized properties of thepolishing pad.
 33. The method of claim 11 wherein the transmittingfurther comprises using a contact ultrasonic transducer to transmitultrasonic signals onto the surface of the polishing pad through thedeionized water.
 34. The method of claim 11 wherein the processingcomprises generating a cross-sectional pad profile based at least inpart on the reflected ultrasonic signals.
 35. The method of claim 11wherein the processing further comprises resolving approximatelymicron-sized properties of the polishing pad.
 36. The method of claim 17wherein the transmitting further comprises using a contact ultrasonictransducer to transmit ultrasonic signals onto the surface of thepolishing pad through a chemical polishing slurry.
 37. The method ofclaim 36 wherein the chemical polishing slurry comprises deionizedwater.
 38. The method of claim 17 wherein the processing comprisesgenerating a cross-sectional pad profile based at least in part on thereflected ultrasonic signals.
 39. The method of claim 17 wherein theprocessing further comprises resolving approximately micron-sizedproperties of the polishing pad.
 40. The method of claim 20 wherein thetransmitting further comprises using a contact ultrasonic transducer totransmit ultrasonic signals onto the surface of the polishing padthrough a chemical polishing slurry.
 41. The method of claim 21 whereinthe transmitting further comprises using a contact ultrasonic transducerto transmit ultrasonic signals onto the surface of the polishing padthrough a chemical polishing slurry.